Manometer



March 30, 1937.

MANOMETER Filed Feb. 11, 1936 Add v62 Emma?) INVEN TO R' ATTO/RNEY A. ZIMMERLI 2,075,326 7 Patented Mar. 30, 1937 UNITED "STATES PATENT OFFICE This invention relates to a manometer ,of the commonly used U gage type, but because of certain novel features of construction the apparatus may be regarded as a precision vacuum gage from Q the standpoint of accuracy of readings, as well as the degree of vacuum which may be measured.

The commonly used U gage consists of two legs connected at their lower ends with either a wide or a constricted tube. One leg is closed, the other is open and can be connected to the vacuum line. When freed from air it is accurate and convenient. It has, however, several drawbacksychiefly:

To'remove all the air it is necessary to boil the mercury under reduced pressure. This is a delicate operation which has to be carried. out by experts, and only specialkinds of glass withstand the treatment. In use, unless special precautions are observed, air is carried into the vacuum leg of the gage, thereby rendering it inaccurate after a. short 'time. To restore accuracy it must be refilled in the manner just mentioned.

If the vacuum is released suddenly it often hap- 5 pens that the impact of the mercury on the glass breaks the top of the closed tube.

If the gage becomes dirty after use it is very diflicult to clean it, so 'that many users prefer to discard it and put a new gage in its place.- 30 It is among the objects of the present invention to provide a dependable manometer which has all the desirable features of the U gage, but is'free from the drawbacks of the latter. That is to say, to provide 'a manometer which can be 35 filled easily and quickly and without boiling the mercury in order to removethe air; one which there is no danger of breaking the-glass if the vacuum is released suddenly; and one so designed that it is practically impossible for air to get 4o-into the system and distortion'of the meniscus by capillary forces is eliminated.

Other objects of the invention have to do with features of construction, method of introducing the mercury into the system, etc. all of which 45 will be apparent from a reading of the following specification.

In accompanying drawing:

The figure is an elevational view showing the assembled glass system and associated parts,

50 while functioning, of a manometer embodying the invention.

Before proceeding with the description attention is directed to the fact that certain of the tubes comprising the glass system are capillary 55 tubes while other tubes forming the gage proper and 4 are sealed to open tubes 6 and 1 respecare large comparatively speaking, and for convenience and sake of clarity these larger tubes will sometimes hereafter be referred to or desig-' nated as noncapillary tubes.

Referringto the drawing, glass tubes I and 2 5 form the legs of the U tube characteristic of vacuum. gages of the present type. The tubes I and 2 are non-capillary, having an internal diameter of 16 mm. and length of 100 mm., and are joined together at their lower ends by a capillary tube 3. 10

The tube 2 is generally referred to in the art as the reference leg of this type .of gage. The upper end of the tube 2 is connected to the bottom of a non-capillary tube 4, by means of a capillary tube 5, which is bent downward to below 15 the bottom of the U, then upward and joined to said tube 4. The interior diameter of the capillary tube 5 is 1.6 mm., while the tube 4 is of the same diameter and length as the tubes I and 2 forming the U. The tops of the tubes I tively, of 6 mm. interior diameter, and said tubes 6 and l are connected by means of heavy rubber tubing, to a three way glass tube 8, commonly known as a T. The gage is connected to a vacuum line by the upper branch of the T.

For accurate and convenient reading of the pressure the gage is provided with metal sleeves 9 and I0, the sleeve 9 being connected to a millimeter scale II, and the sleeve I0 being connected to. a \vernier I2. The adjusting means for operating the sleeves 9 and, I0 may be of any approved construction and for that reason is more or less illustrated conventionally in the drawing. By turning a knob l3 which is mounted on a right and left hand screw I4, one sleeve may be lowered while the other is raised. The screw I5 permits the raising and lowering of both the sleeves 9 and I0 simultaneously. The adjustment of the scales II and I2 will be described more fully hereinafter.

The glass and metal parts may be solidly mounted on a baseor rack (not shownland, a lamp may be supported therefrom to illuminate the glasstubes and scales. The instrument may be fixed on a table or the wall, or held by a clamp.

The reason for choosing a comparatively large 'diameter for the gage is twofold: In the first suppose that it has a volume of 1 cu. mm. at atl amount to 1 mm. or 26%.

of those 100 cu. mm., that is to say the error,

would be .5 mm.

Depending on the accuracy desired, an air bubble of that size may or may notbe objectionable.

For example, at .15 mm. pressure .the error would be .25 mm., that is to say about 1.7% of the absolute pressure, while at 3.8 mm. it would An air bubble at atmospheric pressure of a diameter of .25 mm., which is clearly visible with the naked eye, would cause an error of less than 1% at 2 mm. Even such a small bubble is not left when the gage is 20 filled properly, as hereinafter described.

Filling To fill the gage, pour mercury through the side tube I6 of tube 6 into tube I until tubes I and 2 25 are a little over half full; the level of the mercury should be close to the top of the sleeve II) when the scale is at the zero point. It will take a ut 300 grams of mercury. I

Close the side tube with a piece of rubber hose 0 and a screw clamp, then connect the gage to a good vacuum pump at 8 and exhaust as far as possible. By tilting the gage to one side, then to the other repeatedly, by inclining it backward as far as possible and by tapping the glass sharp- 35 ly, the air adhering to the glass walls is brought to the surface.

When no more air bubbles-are visible, the connections between 6 and-the T, and I and the T are closed by pinching the rubber tube with a screw 40 clamp, without disconnecting the vacuum pump.

The clamp on the side outlet is now carefully unscrewed slightly. The air entering into tube 6 will push the mercury slowly down in tube I and up in tube 2. It should take not less than 1 min--.

45 ute for the mercury level to get to the connection with the capillary tube 5.

When this is reached, the clamp on the side tube I6 is screwed tight, and the gage tilted slowly to the right. This will cause the mercury to 50 flow over the top of the bend into the tubes 5 and 4. when the mercury level in the tube I approaches the bottom, the gage is put back to its vertical position; The screw clamps on the tubes 6 and I are now opened gradually, taking 55 care that no mercury flows over the bend in either direction.

Whenthe pressure is equalized, the pump is shut off and air admitted slowly by unscrewing the clamp on the side tube IS. The mercury will 4 60 rise in the tubes 2 and 5 until the two columns When the pressure decreases to about 120 mm.

in the system, themercury will separate at the top of the bend of tube 5. As the lowering of the pressure affects tubes I and 4 equally, the mer- 75 cury will recede in the tubes 2 and 5,'rlsing at the touch the mercury.

' made by turning knob I3.

same time in the tube I. The mercury column lnthe capillary tube 5 forms a seal between the reference leg 2 of the gage and the vacuum line,

' thus preventing air from getting into the reference leg, which feature is an importantpart of the invention. The diflerence between the levels in tubes I and 2 show the absolute pressure.

To read it, turn knob I3 until the lower edges of the sleeves 9 andIB are atequal distances from the tops of the mercury columns. Now turn screw I5 with a screwdriver until the sleeves seem to The lower edges of the sleeves and the meniscus of the mercury show up against a white backgroundas sharply defined black straight and curved lines respectively. The pressure can now be read directly on scale II. The ver'nier- I2 allows a precision to within .1 mm.

With these adjustments made, the determination of all pressures up to 100 mm. can now be Only occasionally, when the volume of the mercury changes due to operation at different temperatures or after refilling, will it benecessary to adjust screw l5 again. r I

Removal of air Should air get into the system, it will collect at the top of the bend in tube 5. It can be detected, if its volume is too small to be visible as a bubble, by the observation that the two mercury columns do not flow together'immediately when the pressure is increased to about 120 mm.

To remove the air. tilt the gageto the left until the mercury' level in the tube is at the Juncture with the capillary tube. Connect the vacuum pump and the gage; hold in the inclined po-' sition until the mercury separates, Then straighten-the gage; pinch the rubber tube between the tube 6 and the T, and proceed as described for filling the gage.

M odificutions From the foregoing, certain modifications are obvious to those skilled in the art. For example, the dimensions of the tubes comprising the gage proper may be varied within wide limits, as, for instance, the length of the tubes I and2 can be increased if a pressure ofmore than 100 mm. is to be measured, or decreased if only pressures of less than 10 mm. are to be measured.

The diameter of the tubes I and 2 may also be varied; however, it should not less than 12 mm. in order to be free from any capillary influence, and it should be about ten times the diameter of the capillary tube 5. The length of the tube 5 is immaterial provided its lower head is at least as low as the capillary l. The diameter of the tube 4 is generally unimportant; however, it is desirable to ma.ke it Las-lnrge as that of tubes I and 2 in order to reduce the variations of the level of the mercury to a to prevent air from being carried into thecapillary tube 5. For the same reasonsit'is desirable to have the diameter of the tube 3 restricted, al-

though not necessarily a capillary; V I

The T could'be permanently'connected to the gage with glass stopcocks the place'of the rubber tubing and clamps. H

. It is intended to cover all such modifications as I What is claimed is:

- come within the scope of the appended 1. A differential vacuum wi l a'tube system consisting ot'three non-capillary tubes arranged vertically and in transverse alignment, one of said non-capillary tubes having Its 5 of said capillary tube connecting the upp r end of the intermediate non-capillary tube to the lower end of one of the outer non-capillary tubes being at least as low as the other capillary tube connection.

2. A difierential vacuum tube gage comprising a tube system consisting of three non-capillary tubes arranged vertically and in transverse align-'- ment, one ofsaid non-capillary tubes having its opposite ends connected through capillary tubes l5 to the lower ends of the outer non-capillary tubes, the upper ends ot the outer non-capillary tubes being connected to a vacuum line, the lower bend or said capillary tube connecting the upper end of the intermediate non-capillary tube to the lower end of one of the outer non-capillary tubes being at least as low as the other capillary tube connection, mercury in the U-tube formed by the intermediate tube and the non-capillary tube connected to the lower end thereof a mercury seal between the upper end of the intermediate tube and the upper end of the noncapillary tubeconnected to said upper end of the intermediate tube, the space between the seal and the mercury in the intermediate tube being substantially under a vacuum, the difference inthe levels of the mercury columns in said U-tube indicating absolute pressure in said vacuum line, and means for reading said diflerence in level.

ADOLPH ZIMMERLI. 

